C++ keep getting error LNK2019: unresolved external symbol

Question

I tried to google this but always come back with different issues. I am getting 3 unresolved externals when I try to compile this program:

1>main.obj : error LNK2019: unresolved external symbol "public: __thiscall DynIntStack<char>::~DynIntStack<char>(void)" (??1?$DynIntStack@D@@QAE@XZ) referenced in function _main
1>main.obj : error LNK2019: unresolved external symbol "public: void __thiscall DynIntStack<char>::pop(char &)" (?pop@?$DynIntStack@D@@QAEXAAD@Z) referenced in function _main
1>main.obj : error LNK2019: unresolved external symbol "public: void __thiscall DynIntStack<char>::push(char)" (?push@?$DynIntStack@D@@QAEXD@Z) referenced in function _main

DynIntStack.h

/****************************************************************************
DynIntStack class.

Chad Peppers

This class creates a object for stacking nodes

In addition, there should be member functions to perform the following 
operations:
- Push to the stack
- Pop to the stack
- Function to check if empty

****************************************************************************/
// Specification file for the DynIntStack class
#ifndef DYNINTSTACK_H
#define DYNINTSTACK_H

template <class T>
class DynIntStack
{
private:
   // Structure for stack nodes
   struct StackNode
   {
      T value;        // Value in the node
      StackNode *next;  // Pointer to the next node
   };

   StackNode *top;      // Pointer to the stack top

public:
   // Constructor
   DynIntStack()
      {  top = NULL; }

   // Destructor
   ~DynIntStack();

   // Stack operations
   void push(T);
   void pop(T &);
   bool isEmpty();
}; 
#endif

DynIntStack.cpp

/****************************************************************************
DynIntStack class.

Chad Peppers

This class creates a object for stacking nodes

In addition, there should be member functions to perform the following 
operations:
- Push to the stack
- Pop to the stack
- Function to check if empty

****************************************************************************/

#include <iostream>
#include "DynIntStack.h"
using namespace std;

/*************************************************************************
Basic class constructor.

Input Parameters:  Information to build the  stack

Return Type:  void

*************************************************************************/

template<class T>
DynIntStack<T>::~DynIntStack()
{
   StackNode *nodePtr, *nextNode;

   // Position nodePtr at the top of the stack.
   nodePtr = top;

   // Traverse the list deleting each node.
   while (nodePtr != NULL)
   {
      nextNode = nodePtr->next;
      delete nodePtr;
      nodePtr = nextNode;
   }
}

/*************************************************************************
Function to push an item in the stack

Input Parameters:  T

Return Type:  void

*************************************************************************/

template<class T>
void DynIntStack<T>::push(T num)
{
   StackNode *newNode; // Pointer to a new node

   // Allocate a new node and store num there.
   newNode = new StackNode;
   newNode->value = num;

   // If there are no nodes in the list
   // make newNode the first node.
   if (isEmpty())
   {
      top = newNode;
      newNode->next = NULL;
   }
   else  // Otherwise, insert NewNode before top.
   {
      newNode->next = top;
      top = newNode;
   }
}

/*************************************************************************
Function to pop an item in the stack

Input Parameters:  T

Return Type:  void

*************************************************************************/
template<class T>
void DynIntStack<T>::pop(T &num)
{
   StackNode *temp; // Temporary pointer

   // First make sure the stack isn't empty.
   if (isEmpty())
   {
      cout << "The stack is empty.\n";
   }
   else  // pop value off top of stack
   {
      num = top->value;
      temp = top->next;
      delete top;
      top = temp;
   }
}

/*************************************************************************
Basic class deconstructor.

Input Parameters:  None

Return Type:  void

*************************************************************************/
template<class T>
bool DynIntStack<T>::isEmpty()
{
   bool status;

   if (!top)
      status = true;
   else
      status = false;

   return status;
}

main.cpp

#include <iostream>
#include "DynIntStack.h"
using namespace std;

int main(){

    int value = 0;
    char value2;
    //DynIntStack<int> stack;
    DynIntStack<char> stack1;

    cout << "Pushing 1\n";
    stack1.push('T');
    stack1.pop(value2);
    cout << value2;

    system("pause");
    return 0;
}

score 17 · Accepted Answer · answered Apr 22 '12 at 20:26

17

You need to put all the template implementations that you have in your .cpp file in the header file, or in a file included by the header. And don't try to compile the implementation file. Some systems attempt to compile files with a .cpp suffix. The compiler needs to see the code in order to instantiate templates.

answered Apr 22 '12 at 20:26

juanchopanza

223,364
34
402
480

1

If I had a pound for everytime I see this question – EdChum Apr 22 '12 at 20:27
@EdChum or an upvote :-) – juanchopanza Apr 22 '12 at 20:27
Very frustrating! That is only on templates? – chadpeppers Apr 22 '12 at 20:33
1

@Chad yes. Think of templates as partial code that needs specific template arguments at compile time in order to be instantiated. The compiler basically makes code out of the template. This has to happen before compilation. I hope that made sense... – juanchopanza Apr 22 '12 at 20:35

score 5 · Answer 2 · answered Apr 22 '12 at 20:27

5

at the bottom of DynIntStack.h, put

#include <DynIntStack.cpp>

what's happening is the compiler doesn't see the template implementation code so cannot emit anything for it.

answered Apr 22 '12 at 20:27

stijn

34,664
13
111
163

score -1 · Answer 3 · answered Oct 06 '14 at 10:05

-1

The most simplest solution to the problem is:

Wherever you want to include your template class e.g. "DynIntStack.h" instead do "DynIntStack.cpp". e.g. in your main.cpp above.

Simple as that, no need to change anything else.

answered Oct 06 '14 at 10:05

revolutionary

3,314
4
36
53

1

Why is this answer voted down since the solution actually works? – Karol Borkowski Apr 04 '20 at 13:33
Other answers say the same thing, and 2 years earlier. – Oskar Skog Apr 25 '20 at 15:29

C++ keep getting error LNK2019: unresolved external symbol

3 Answers3

Linked